1. Field of the Invention
The present invention relates to a radio transmitter adapted to change its communication mode by externally downloading a predetermined software and, in particular, the present invention relates to a radio transmitter adapted to prevent a radio signal which is incompliant with (does not comply with) a predetermined standard from being transmitted.
2. Description of the Related Art
Recently, there is proposed a software radio transmission technology by which a radio transmitter can cope with a different communication mode by downloading a software associated with the different communication mode via a wire communication or a radio communication from outside. A conventional radio transmitter using the software radio transmission technology will be described with reference to FIG. 7. FIG. 7 is a schematic block diagram illustrating an exemplary one of conventional radio transmitters. The conventional radio transmitter comprises: a CPU 101, a memory 102, a modulation section 103, a D/A section 104 and a transmitter section 105.
The memory 102 is comprised of a fundamental software storing region and a communication mode software storing section. What is meant by the fundamental software is a software required for a basic operation of the radio transmitter. Furthermore, what is meant by the communication mode software is a software required for a modulation and the like and may previously be written into the memory 102. The CPU 101 is configured to control the radio transmitter itself according to the fundamental software and store a communication mode software into the memory 102 when the communication mode software is inputted via wire communication or radio communication from the outside.
In a transmission operation of the radio transmitter, the CPU 101 functions to output the communication mode software stored in the memory 102 to the modulation section 103. In response thereto, the modulation section 103 functions to output a digital modulation signal which is modulated according to the communication mode software to the D/A section 104. The D/A section 104 functions to convert the digital modulated signal to an analog modulation signal and thereafter output the latter to the transmitter section 105. The transmitter section 105 functions to process the analog modulation signal by a frequency conversion, a electric power amplification and a band limitation and then output it to the outside as a radio signal. It should be noted that a radio signal to be transmitted must be compliant with predetermined standard or standards required for a radio law and a system operation.
Normally, a decision whether or not a radio transmitter is compliant with (complies with) various standards required for the radio law and the system operation is performed at the shipment time of the radio transmitter or periodically after that shipment by its manufacturer. However, it is not surely clear that a radio signal to be transmitted by using the software radio technology will be transmitted with absolutely right spectral because its communication mode changes in response to a kind of the downloaded communication mode software.
Furthermore, there is a fear that, during a transmission of a radio signal from the radio transmitter, a leakage power between adjacent channels tends not to be compliant with the standard required for the radio law and the system operation due to, for example, a deterioration with time and an unpredictable factor occurred in the radio transmitter. Still further, although a communication mode software is downloaded normally with an authentication for a safety purpose, there is a possibility that an injustice communication mode software due to the computer virus or the like will be downloaded, as a result of which a radio signal which is incompliant with the standard may be transmitted. In the event that such a radio signal incompliant with the standard has been transmitted, it is expected that a communication for a user who uses its adjacent channel for example is disabled. However, it is impossible for the conventional radio transmitter to stop a transmission of such a radio signal incompliant with the standard or issue an emergency or abnormal alarm.
In order to address the above-mentioned problems, an object of the present invention is to provide a radio transmitter capable of normally monitoring a radio signal to be transmitted, stopping the radio signal transmission and outputting an emergency alarm in event that the radio signal is incompliant with a predetermined standard.